The Role of the RNA-binding Protein PABPC1 in Endothelial Gene Expression and Angiogenesis

Project Summary Cardiovascular diseases are the primary cause of death around the world. Many such diseases involve a restriction of blood flow to critical organs resulting in tissue death. There are also currently limited options for treatment and there remains a significant need to discern the mechanisms of the angiogenic response. Angiogenesis, the formation of new blood vessels from existing vasculature, involves intricate regulatory mechanisms. RNA-binding proteins are among these regulators, yet their role in endothelial cells (ECs) and angiogenesis remains poorly understood. Using an in vitro loss-of-function screen, we identified the RNA binding protein Poly(A) binding protein cytoplasmic 1 (PABPC1) as a key regulator of angiogenesis. We then generated EC-specific PABPC1 knockout (iECKO) mice to study the role of PABPC1 in angiogenesis in vivo. We discovered reduced vascular progression and increased immune cell infiltration during neonatal retinal angiogenesis of PABPC1 iECKO mice. Our preliminary data suggest the roles of another RNA-binding protein ZFP36 and the chemoattractants CXCL1 & 8 in mediating observed phenotypes. It also suggests PABPC1 might regulate this process by binding to and enabling the function of ZFP36. Hence, we hypothesize that endothelial PABPC1 regulates angiogenesis through binding with ZFP36 to affect both mRNA stability of CXCL1 & 8 and immune cell infiltration. To test our hypothesis, we will first determine in human cell culture models if PABPC1 suppresses CXCL1 or 8 mRNA in ECs by binding to the mRNA decay protein ZFP36 (Aim 1). We will also further characterize the PABPC1iECKO retinal phenotype and determine if upregulated expression of the chemoattractant CXCL1 (mouse homolog of human CXCL1 & 8) mediates immune cell infiltration and reduced angiogenesis in PABPC1iECKO mice (Aim 2). The training in this proposal will focus on developing skills to produce a successful independent investigator including project development, execution, and data analysis. New techniques will be learned and utilized during this project including immunohistochemistry, cloning, and animal handling. Our lab has access to the vast resources of the MCW Physiology department as well as experts in cardiovascular biology, gene expression regulation, and RNA biology.